Lithium ion secondary batteries used in automotive vehicles are required to have high performances and a longer life as compared with other general-use lithium ion secondary batteries. Thus, impurities such as water need to be maximally removed.
To this end, in JP2009-266739A, electrodes of a necessary length are produced by cutting a coiled electrode and a power storage element is formed by successively laminating the produced electrodes and separators. Before the power storage element is inserted into an exterior material and an electrolyte liquid is injected, the power storage element is dried to remove moisture included in the electrodes.